Most earth drilling systems employ some form of rotary or percussion powered drills. There have been many advances in recent years to make the drilling operation more efficient, and thus provide better and faster drilling speeds, especially in rock layers. Typically, a drilling machine, such as for forming a hole for an explosive charge, or for anchoring a roof bolt, includes a drill stem with a drill bit on the distal down hole section thereof. The stem/bit on a rotary drill machine is rotated by a spinner mounted on a drill head to form the drill hole. The rotary driving motion of the spinner is usually hydraulically or pneumatically driven and manually regulated by the operator of the drill machine. Due in part to the advances in the technology, such as in regard to the drill bit and/or components of the drilling machine, providing attendant easier and faster drilling, operators have become accustomed to set the controls to try to drill the hole in the least amount of time. In doing so, the spinner head is rotated and the feed of the drill head is engaged to move the drill stem into the hole as rapidly as possible. The operator typically changes these settings only in the event that a problem develops.
As a part of the more efficient drilling, the cuttings and dust must be collected and removed from adjacent the drill bit so that clean cutting edges are provided at the bottom of the hole to allow the most efficient contact with the rock, or other strata. Typically, a pneumatic or hydraulic cuttings/dust collection/suppression and removal system is employed. Pressurized air, or a suitable hydraulic fluid such as water, or an air/water mixture, is forced down a center passage through the drill stem to bail or pick up the cuttings and dust for disposal. It is also known to impose a vacuum on the center passage of the drill stem drawing air into the hole around the periphery of the drill stem, whereupon the cuttings and the dust particles are entrained and removed through the center passage. In either system, this withdrawn debris is pneumatically or hydraulically conveyed away from the drill hole. When using air, the cuttings and dust are then filtered out at a remote location and disposed of. In systems where water is used, either exclusively or in a mixture with other fluids, an option is to simply allow the dust to be suppressed and then deposited outside the drill hole. In either case, airborne contamination is advantageously substantially eliminated.
A typical drilling arrangement and cuttings/dust collecting system is shown in the prior art; Howeth, U.S. Pat. No. 4,434,861. In this patent, the bailing air is supplied through the center passage of the drill stem and the cuttings/dust is removed from the hole by a vacuum head. Insofar as the '861 disclosure is concerned, the advancement of the drill stem into the hole, and the rotation of the drill bit, are manually controlled by the operator. Other functions of the drilling system are however automatically controlled, such as the extending or retracting the drill stem with respect to the deck plate. In other words, the drill stem extends to the drilling position only when the drill stem is supplied with sufficient bailing air to be operative, and the drill stem is automatically retracted from the hole when the bailing air supply is terminated (see column 14, lines 14-37).
Another feature of the prior art Howeth '861 patent is to provide an improved vacuum skirt around the hole and the drill stem so as to attempt to improve the sealing, and thus enhance the efficiency of the bailing operation by reducing the tendency of the bailing system to choke or overload. This patent also teaches the fundamental premise of making certain that the passageways are proportioned sufficiently larger than the drill hole to also help alleviate choking of the bailing air carrying the cuttings/dust (see column 14, lines 38-66). While this overall system is an improvement over prior art drilling machines, problems still arise with regard to choking or overloading the vacuum system, especially where the drill speed is increased beyond normal levels and when strata containing soft minerals, coal, shale, mud stone or the like debris are encountered in the drilling operation.
Other patents, such as the patent to Ek, U.S. Pat. No. 3,946,818, have disclosed other efforts of inventors to improve the sealing of the skirt in a different manner to try to improve the flow so that choking does not occur as readily. Heretofore, approaches other than these stop gap methods to solve the same problem have simply not been successful, insofar as we are aware. In theory, the operator of the drilling machine is simply depended upon to try to anticipate any approaching choking or flow overload situation and then shut the machine down. Unfortunately, in an overwhelming percentage of times, this is not possible because of the response time factor, and the collecting system becomes overloaded. The entire drilling operation must then be shut down for an extended period, the drill stem and bit removed from the drill hole and all passageways cleared of the debris. Alternatively, drilling must be performed at a continuously reduced rate to compensate and thus prevent these intermittent overload conditions.
Other inventors have concentrated on improving other aspects of the drilling machines, such as with respect to an improved cyclone filter, as set forth in the England U.S. Pat. No. 5,320,188. Indeed, there have even been attempts to control the flow of pneumatic fluid to the drilling tool in an automatic fashion. In the McDonald et al. U.S. Pat. No. 4,936,397, the pneumatically controlled valve is operable to transmit an initial, extra strong pulse of air to initiate operation of the down hole drilling motor. Once the motor is operating, the valve is kept open at a lower pressure than is required to open it so that the drilling can continue at a lower energy level.
Similarly, energy saving is the impetus in the Enlund et al. U.S. Pat. No. 5,409,072, wherein the pneumatic air supply is provided by a compressor driven by a hydraulic drive motor with adjustable displacement. The pneumatic pressure supplied by the compressor is adjusted inversely proportional to the pressure primarily used to drive the percussion drill along its linear path, and/or the input pressure of the drive motor itself. In this manner, it is proposed that the energy required to operate the entire system is maintained substantially constant during all phases of the operation.
Thus, while many refinements have been made in drilling machines and their method of operation, there is a marked absence of more responsive control systems, and more particularly with regard to regulating the drill feed and rotation in response to one or more parameters occurring in the cuttings/dust collecting or suppression system. Such a concept would have specific usefulness in improving the drilling efficiency especially for forming small (20-50 mm) diameter holes using rotary cutting tools and high tool feed forces. In such an arrangement, we have discovered that it would be especially advantageous to keep the drill penetration rate as rapid as possible, while at the same time control the rate of tool advance and/or rotation using feedback from the cuttings/dust collection or suppression system. In this manner, it is believed that clogging or overload, and its deleterious side effects, can be avoided. What we envision as a need in the underground mining industry, and particularly for drilling small diameter holes for installation of roof bolts, explosive charges or the like, is such an automatic control, but through a system that is simple in design and operation.
Accordingly, it is a primary object of the present invention to provide an improved in-situ drilling system, and related method having a control system for maximizing drilling efficiency, primarily by preventing overload through efficient removal of the cuttings/dust for collection or suppression by means of a flushing mechanism, and in addition, substantially eliminating airborne dust contamination.
It is another object of the present invention to provide a highly efficient design for such a system and one that is effective in operation to anticipate overload by sensing a change in an operating parameter in the flushing mechanism.
It is another object to provide a drilling system that makes a provision to sense a parameter of the fluid used for removal of cuttings and dust, and then through a feed back signal to a controller regulate the feed rate of the drill head and/or the rotation of the spinner.
It is still another object of the present invention to provide such an apparatus and its method for providing substantially continuous in-situ drilling, wherein the drill cuttings and dust are removed from the drill hole, and either collected and disposed of or suppressed in a highly efficient manner, with control being dependent upon the change in pressure, flow or other parameter in the flushing mechanism, so that the drill stem and drill bit are maintained in an optimum operating mode.
Still another object of the present invention is to provide a drilling system wherein an approved, low power control circuit is utilized with a programmable controller to monitor the negative or positive gauge pressure in the fluid flushing mechanism, and provide a responsive signal to the feed device for the drill head and/or the rotary drive of the drill stem to efficiently control the drilling operation to virtually eliminate downtime due to clogging or overload.
Yet another object of the present invention is to provide an apparatus and method of the type described wherein the controller is programmable to allow adjustment of the approaching overload, and other conditions of the drilling operation.
It is still another object of the present invention to provide a drilling system utilizing a feed device for the drill head and a rotary spinner for driving the drill stem and the drill bit, and wherein the rate of feed of the drill head and/or drill rotation is effectively controlled based on the level of a sensed parameter of the fluid flushing mechanism so as to detect an approaching overload condition, whereby drilling system downtime is avoided.
Additional objects, advantages, and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects of the invention, and in accordance with the purposes thereof, an improved apparatus and method for controlling the operation of a drill stem and drill bit based on monitoring the status of the fluid flushing mechanism is provided. More specifically, the apparatus provides for substantially continuous in-situ drilling, collecting and disposing or suppression of the drill cuttings/dust by feedback of the level of negative or positive gauge pressure maintained in the flushing mechanism through a programmable controller. The control circuit is preferably a low power (4-20 ma) electronic circuit that is approved for all underground mines. Alternatively, a hydraulic or electro-hydraulic circuit providing a comparable function is contemplated. The inventive system is targeted primarily for small (20-50 mm) holes in virtually any type of mining operation, including soda ash, coal, trona, salt, potash, limestone, gypsum or the like.
In this preferred embodiment for carrying out this principle, there is provided a drill stem having a drill bit, a drill head for feeding the stem/bit to form the drill hole, a mechanism for flushing the cuttings/dust from the hole and conveying it to a remote location. A transducer tracks at least one parameter of the flow in order to provide a signal to the controller for regulating the rate of drilling so as to anticipate an approaching overflow condition. By utilizing such a system, the cuttings/dust and other debris are efficiently removed to eliminate or minimize airborne contamination. This objective is accomplished in a controlled manner without ever reaching an overload condition in the flushing mechanism that could lead to clogging and downtime of the drilling system.
Also, in the preferred embodiment the parameter is sensed through the transducer coupled to a transfer duct of the flushing mechanism. The feedback arrangement provides for a corresponding signal to be generated by the transducer indicative of the pressure in the duct. In return, the controller is operative to regulate the operation of the feed device for the drill head to vary the rate of feed dependent on the signal level. In addition, the drive unit for rotating the drill stem/bit can be controlled in concert with the feed.
Given the objective requirement for simplicity, the flushing mechanism includes for vacuum generation a standard blower connected to the transfer duct through a standard filter. The filter may include tortuous path, cylinder cartridges and/or cyclone filters. The filters are periodically emptied/cleaned to dispose of the larger particles of the cuttings, as well as the smaller dust particles.
The controller can be used to program and adjust the threshold of the approaching overload so that maximum drilling efficiency is obtained for any particular mining, or related operation, being performed. The window of operation is set to insure substantially continuous drilling and eliminate false signals of approaching overload. The upper and lower thresholds of the gauge pressure in the flushing mechanism can be varied to establish the optimum rate of feed and/or drilling rotation.
In an alternative embodiment, the flushing mechanism utilizes pressurized fluids, such as including water, that is pumped through the center passage of the stem/bit. A slurry of cuttings/dust is formed and forced out of the drill hole for easy disposal, while in effect suppressing the dust to eliminate airborne contamination. Any increase in positive gauge pressure is sensed through the transducer in the transfer duct to anticipate any approaching overload condition. As in the preferred embodiment, corrective adjustment is automatically made in the drilling rate.
With respect to the related method of the present invention, the in-situ drilling and collecting or suppressing of the drill cuttings and dust from the drill hole includes the steps of drilling the hole with a drill stem and bit, flushing the cuttings/dust from the drill hole, monitoring at least one parameter of the flow of the bailing fluid, and regulating the rate of drilling to control the parameter during both a normal and approaching overflow condition. By use of this method, the drilling operation can be continuous as the collection or suppression of cuttings and dust from the drill hole is carried out in a controlled manner.
In accordance with the preferred version of the method, the parameter being monitored is the vacuum or negative fluid pressure level in the flushing mechanism. The regulating step is preferably concerned with the rate of feed of the drill stem into the drill hole. That is, the feed rate, including from zero to maximum, is made dependent on the signal level of the negative gauge pressure sensed in the transfer duct during the step of collecting and conveying the cuttings/dust or otherwise suppressing the dust. As an additional feature, the use of a programmable controller, or an equivalent adjustable operating hydraulic or electro-hydraulic valve, allows the addition of the step of adjusting the threshold of the approaching overload of the flushing mechanism for maximum efficiency. Also, adjustment of the reset window of the gauge pressure is contemplated. Close control of the threshold and the reset window helps in establishing the optimum rate of feed for the drill to stem and thus the drilling efficiency. In more specific terms, in the case of vacuum flushing, the adjusting step is performed by setting the threshold level of the vacuum/negative gauge pressure in the range of 10% to 20% above the normal negative pressure level, and to reset to normal vacuum within 0.5-4 inches Hg. as the threat of the overload is passed. If desired, the regulating step can include changing the speed of the rotary driving of the drill stem, also depending on the signal level from the transducer and coordinated with the linear feed rate of the drill stem.
Thus, under optimum operating conditions, the regulating step can perform so as to maintain the parameter in the flushing mechanism, such as the vacuum level or rate of flow of the fluid, so as to be substantially constant. Also, while the regulating step, as controlled by the programmable controller, can be made to vary the drill head feed and the spinner rotation, the preferred embodiment at present is to actually stop the feed of the drill stem and/or the spinner during an approaching overload condition, and to automatically restart the feed/rotation at the optimum rate when the potential or threatened overload condition is past.
Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments, and its several details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.